Process for the vulcanization of rubber and double bond containing rubberlike elastomer compositions containing fillers



Jan. 30 1968 H. WESTLINNING ETAL 3,366,598

V PROCESS FOR THE VULCANIZATION OF RUBBER AND DOUBLE BOND CONTAININGRUBBERLIKE ELASTOMER COMPOSITIONS .GONTAINING FILLERS o ,qcc A2/97a?Filed Dec. 23, 1965 :5 l 7 #5gg/4,55*

United States Patent O 3,366,598 PROCESS FOR THE VULCANIZATION F RUBBERAND DUBLE BND `COllI'AllJING RUBBER. LIKE ELASTMER COMPOSITIONSlCONTAIN- ING FILLERS f Hermann Westlinning, Kleinostheim, SiegfriedWolfi",

Bruhl, Bezirk Cologne, and Werner Schwarze, Frankfurt am Main, Germany,assignors to Deutsche Goldund Silber-Scheideanstalt vormals Roessler,Frankfurt am Main, Germany Filed Dec. 23, 1965, Ser. No. 516,025 Claimspriority, application Germany, Dec. 24, 1964,

7 claims. (cnf 26o-41.5)

The present invention relates to a process for the vulcanization ofrubber or double bond containing rubber-like elastomer compositionscontaining fillers, such as, carbon black, silica and silicates.

In order to obtain the optimum properties in vulcanizates of rubbercompositions containing reenforcing fillers vulcanization systems areusually employed which are built up of a large number of components. Inaddition to the elastomer and the more or less active reenforcing fillerthey contain one or more vulcanization accelerators, usch as, forexample, 2,2dibenzothiazyl disulfide, Z-mercaptobenzothiazole, diphenylguanidine and others, sulfur, zinc oxide, stearic acid, antioxidantsand, if desired, softeners. The complicated systems indicated above allhave proved good for the vulcanization of carbon black containing rubbercompositions. They, however, more or less fail when the so-called lightfillers, such as, especially active reenforcing silicas, are employedand vulcanizates are desired which are primarily subjected to dynamicstresses rather than static stresses. In view of the consideration thatthe active light fillers more or less strongly absorb the acceleratorsand they 3,366,598 Patented Jan. 30, 1968 ICC particularly the number ofreactive hydroxyl or silanol groups present, plays a role in disturbingthe vulcanization reaction when nely divided silicia is used, `attemptshave been made to provide vulcanization conditions by modification ofthe filler surface characteristics which during the course of thevulcanization reaction and in the properties of the vulcanizationobtained correspond to those of the conventional vulcanization of carbonblack filled mixtures. It was found, however, that the improvementsattained by such surface modification in no way lead to lightvulcanizates with the properties of the carbon black vulcanizates,especially with regard to the properties concerned under dynamicstresses. The increased vulcanizing agent requirements which occur inmany instances even with surface modified silicas,

" permits the conclusion that the surface modification does arewithdrawn thereby from their primary function in the vulcanizationprocedure, it has been customary to I:increase the quantities of theaccelerators employed some 50 to 500% over the quantities normallyemployed in carbon black filled compositions. Aside from the fact thatthis increased requirement for accelerators,

which in part are costly substances, is an economic disadvantage, theproperties of the vulcanizates obtained still do not meet therequirements which are made today for carbon black filled vulcanizates,for example, in abrasion loss values or the moduli. v

Very extensive investigations of the non-accelerated and acceleratedvulcanization of non-filled and carbon black filled mixtures have'confirmed the necessity of additions of Zinc oxide and stearic acid inorder to increase the yield of cross-linking bridges and the velocity ofthe vulcanization, but other tests have also shown that the course ofthe vulcanization procedure with mixtures filled with light reenforcngfillers does not undergo any essential change whether in the presence orabsence of zinc oxide and stearic acid. The absence of the zinc sulfidesulfur, the presence of which is characteristic for an `undisturbedvulcanization reaction, the presence of which can always be detectedwhen zinc oxide and stearic acid take part in cross-linking reactionwhich is the basis for the vulcanization, permits the conclusion that,when finely divided silica or equivalent fillers are used, the partialreaction between the zinc oxide or respectively stearate and the activegroup of the accelerator, for instance, a benzothiazyl radical, which isessential for the conventional vulcanization of nonfilled or lcarbonblack filled mixtures, does not occur. The result of this is that in thepresence of light fillers, cross-linking primarily occurs by theformation of thioether-like or disulfide bridging bonds.

As evidently the surface characteristics of the filler,

not ensure that disturbances during vulcanization do not occur.Furthermore, when it has been possible to normalize the character of thevulcanization by modification of the surface characteristics of thelight filler, this also has led to a very considerable decrease in theoriginal reenforcing properties of the filler.

According to the invention it was unexpectedly found that avulcanization reaction could be achieved which overcomes thedifficulties encountered in vulcanizations with conventionalaccelerators, especialy in the Ipresence lof light reenforcing fillerseven Without modification of their surface characteristics when certainderivatives of 1,3,5-triazine are employed instead of the conventionalaccelerators.

According to the invention the vulcanization of reenforcing fillercontaining compositions of rubber or rubber like elastomers which stillcontain double bonds is carried out With the aid of a vulcanizationsystem which invaddition to sulfur contains a 1,3,5-triazine of thefollowing general formula )Ir t i Yl-s-d C-s- Z in which n signifies aninteger of from l to 20, preferably 1-10. X signifies: hydrogen, alkyl,alkenyl, aryl, or aralkyl groups which can be attached directly to thering or over heteroatoms or heteroatom groups such as, for exa-mple,-O-,-S-, -NH-, -NHSOT- and NH-NH- and which also may be substituted.

Each of Y and Z taken individually signifies:

(Il) y hydrogen (b) -S-R The new vulcanization system according to theinvention can be used to vulcanize reenforcing filler containingcompositions of natural and synthetic rubber as well as double bondcontaining rubber like elastomers.

The properties of the vulcanizates produced with the vulcanizationsystem of the invention can in every respect be compared with thoseobtained with conventional vulcanization systems or surpass them'. Thenew vulcanization system especially renders it possible-depending uponthe surface characteristics of the ller concernedto provide, by suitableselection of the substituent X, an optimum adjustment of the reenforcingsystem and the vulcanization system with respect to ea'ch other whichmanifests itself in high tearing strengths, moduli or elasticities. Anespecial advantage of using the triazine compounds according to theinvention is that the difficulties which usually occur in thevulcanization of mixtures containing light reenforcing fillers,especially active silicas, with conventional accelerators are overcomeand that very good vu-lcanization properties also upon being subjectedto dynamic stresses are achieved. The improvement attained in the use ofthe vulcanization system of the invention above all resides in thedecrease of the number of the reaction steps up to the cross-linking,

in the formation of polysuldic cross-linking bridges or cross-linkingbridges of equivalent behavior, even in the presence of finely dividedsilica or silicates and in a farreaching similarity to the`cross-linking structure which is obtained with an undisturbedvulcanization through which the modication reactions of the polymer,which are also desired, are caused.

The compounds included in the following are illustrative of the seriesof functional triazine compounds which are suitable `for thevulcanization system according to the invention.

Such table identities the substituents X, Y and Z, as well as the numbern, in the compounds concerned which are of the following formula:

Y -S-o C-s- Z N Those which have been ascribed a V number are referredto later in the application with reference to such number.

1 Statistically -4 (average mol wt. 1,010). 2 Statistically -2 (averagemol wt. 400). 3 Statistically -8 (average mol wt. 1,705).

The mercapto triazine compounds are employed according to the inventionin quantities between 0.3 and 6.0 and preferably between 0.5 and 4.0parts by weight per 100 parts by weight of rubber. In general, goodresults are obtained in quantities which about correspond to those ofthe known vulcanization accelerators in conventional vulcanizationsystems.

The quantity of sulfur is analogously determined and the vulcanizationsystem can contain up to 6 parts by weight of sulfur per 100 parts byweight of rubber. In general, however, about 0.5 to 3 parts by weight ofsulfur are used.

As can be seen from the examples the ratio between both components ofthe Vulcanization system, that is, between the triazine compound and thesulfur, can be selected as desired. Advantageously, however, higherquantitiese of the triazine compound are employed with lower quantitiesof sulfur or vice Versa. In connection therewith it was found that,especially, with higher sulfur quantities, vulcanization assistants suchas zinc oxide and stearic acid can be added to the mixture Vwithoutdisturbing the progress of the vulcanization to any noteworthy extent.It is also possible to employ conventional accelerators in combinationwith the vulcanization system according to the invention.

Various filled rubber Vvulcanizates were prepared in the followingexamples with representative compounds taken from Table A and comparedwith Vulcanizates produced with conventional accelerators. The results0f the investigations of the properties of the vulcanizates are given inTables 1-10 which respectively are appendices to Examples l-lO.

In all instances mixtures were employed which contained 50 parts byweight of ller per 100 parts by weight of elastomer. The quantities ofaccelerator, S, St (stearic acid) and ZnO employed are given in parts byweight per 100 parts by weight of elastomer. The iiller, type ofelastomer, accelerator and vulcanization temperature are identied in theindividual tables. The accelerators according to the invention areidentified with reference to the V numbers given in Table A. Theconventional accelerators Vulkazit CZ:N-cyclohexyl-Z-benzothiazolesulfonamide Vulkazit DM=2,2-dibentothiazyl disuliide Vulkazit D=diphenylguanidine are identied by reference to the letters CZ, DM and Drespectively. The carbon black employed was a furnace black of gradeHAF. The silica employed was a highly active silica obtained by Wetprecipitation methods of a specic surface area of about 240 m.2/ g.,having a primary particle size below 100,u.. The control tests withconventional accelerators are in each case identified in the tables bythe appearance of in the iirst column.

Example 1 The rubber used in this example was a mixture of astyrene-butadiene rubber with about 24% of styrene (designated as BH 150in Table 1), furnace black (HAF), using trazine compound V and sulfur inthe quantities indicated in Table 1. The Vulcanization tem perature was160 C.

Example 2 The rubber used in this example was an oil extended butadienestyrene rubber designated as BH 302 in Table 2. Triazine compound V25and sulfur Were again used in this example.

Example 3 The series of tests which are the basis of this example andthe tabulated results given in Table 3 were carried out in the samemanner as the tests carried out in Examples 1 and 2. In this instance,however, 1,4-cispoly butadiene was employed as the elastomer.

Example 4 In this example the triazine compound employed as theaccelerator was compound V19. As can be seen from Table 4 it is alsopossible in this instance especially to cause substantial increase inthe modulus values as comparable values for the tearing strength.

Example 5 In this and the following examples a highly active SiO2 wasemployed in place of the carbon black of the previous examples. Thetriazine compound employed was Compound Vl9. It will be seen bycomparison of the tabulated results given in Table 5 that considerableincreases in tearing strength and modulus values over those of thecontrol Which was vulcanized with Vulkazit DM and D, sulfur, zinc oxideand stearic acid were obtained.

Example 6 In this example the triazine compound employed again wascompound V19. The rubber used was an oil extended butadiene-styrenerubber. The results are tabulated in Table 6.

Example 7 In this series of tests the triazine compound again wascompound V19 but the rubber employed was 1,4-cis-polybutadiene. Theresults are tabulated in Table 7.

Example 8 The rubber employed in this series was the styrenebutadienerubber designated as B 150. The triazine compound Was compound V25. Ascan be seen from Table 8, even with low quantities of sulfur (128 parts)and of compound V25 (0.54 part), the modulus values are considerablyhigher than those of the control, whereas the tearing strengths arepractically the same.

Example 9 Oil extended butadiene-styrene rubber designated as BH 302 andtriazine compound V25 were used in this series. The results which aregiven in Table 9 indicate in this instance the improvement in mechanicalproperties was not confined to the modulus values and the tearingstrength. The shore hardness was also raised slightly.

Example 10 TABLE 1 (EXAMPLE 1).-RUBBER=BH 150. VULCANIZATION TEMP. 160C.

Batch No. Heating Tearing Modulus, Elongation Modulus filler: Acceler- SSt ZnO time, strength, Percent, Percent on break, Elasticity, Shorecarbon ator min. lig/ein.2 kg./c1n.2 Percent Percent hardness black 300%500% 1.25 CZ 1. 60 246 25 75 410 30 0.54 V25 3. 84 20 218 38 106 340 320.54 V25 2. 56 40 170 39 107 290 34 0.54 V25 1. 28 S0 242 30 77 420 341.08 V25 3. 84 40 226 66 189 230 32 1.08 V25 2. 56 20 215 30 110 300 341.08 V25 1. 28 60 271 34 95 405 36 2.16 V25 3. 84 20 250 70 198 240 352.16 V25 2. 56 20 238 71 147 283 35 2.16 V25 1. 28 40 262 55 113 353 363.24 V25 3. 84 20 202 101 185 34 3.24 V25 2. 56 20 225 57 116 280 363.24 V25 1. 28 40 210 42 112 300 37 TABLE 2 (EXAMPLE 2).-OIL EXTENDEDBUTADIENE-STYRENERUBBER BH 302. VULCANIZATION TEMP. 160 C.

B atch N o. Heating Tear-ing Modulus, Elongation Mo dulus fillerAcceler- S St ZnO time, strength, Percent, Percent on break, Elastiety,Shore carbon ator min. kgjcm kglem.2 Percent Percent hardness black 300%500% 1.25 CZ l 1. 75 2.0 3.0 60 202 15 53 473 21 61 1.08 V25 2. 56 20199 24 77 378 26 58 2.16 V25 1. 28 40 206 22 75 400 27 63 Modulus Impactresistance, kg./cm. 300% 500% Shore hardness Elasticity, percentElongation on break,

percent Modulus P ercent lig-Jem.2

TABLE 3 (EXAMPLE 3).-POLYBUTADIENE RUBBER CB. VULCANIZATION TEMP. 160 C.

Heating Tearing time, strength, percent, min.

ZnO

0 s w u .00 l u d o M 0 0 3 t c. I aem D .SMJ mmag T. k ms Or ha Shr .kmwwe 1mm EUG p t an y 50km H nlC One i.wre Etbn. t 4 1784300691 e 1 1 111. m P S y2. 3 830441672 2 433554655%:9UM ueC m7 eg Mpk ghfo.. 7810940305227 5 o6-037 0 l 1 111.11%k1n2mn n/ e Tg Mk UD 0 00000006000.mnvl t 6 66646624622@ .mmm ..11 mtu 0 O A 1 3 1 Z 0 2 TABLE 4 (EXAMPLE4).-RUBBER 13H 150. VULCANIZATION TEMP. 160 C.

Accelerator TABLE 5 (EXAMPLE 5).-BUTADIENE-STYRENE-RUBBER BH 150.VULCANIZATION TEMP. 160 C.

Accelcrater Modulus ModulusV Modulus Shore hardness Shore hardness Shorehardness Elongation on break, Percent Elongation on break, PercentElongaton on break, Percent Modulus, Percent, kg./c1n.2

Modulus, Percent, lig/cm.2

Modulus, Percent, kg./cm.2

Tearing strength, lig/cm,2

Tearing strength, kgjcm.2

'Fearing strength, kgJcm.2

Heating time,

' min.

Heating time, min.

Heating time, min.

Accelerator TABLE 7 (EXAMPLE 7).-POLYBUTADIENE RUBBER CB. VULCANIZATIONTEMP. 160 C.

Accelerator TABLE 8 (EXAMPLE 8).--BUTADIENE-STYRENE-RUBBER BH 150.VULCANIZATION TEMP. 160 C.

Accelerator TABLE 6 (EXAMPLE 6).-OIL EXTENDED BUTADIENE-STYRENE-RUBBERBH 302. VULCANIZATION TEMP. 160 C.

ller2= S102 Batch No. filler: S102 ller= S102 BatchNo,

BatchNo.

TABLE 9 (EXAMPLE 9).-OIL EXTENDED BUTADIENE-STYRENE-RUBBER BH 302.VULCANIZATION TEMP. 160 C.

Batch No. Heating Tearing Modulus, Elongation Modulus filler= Acceler- SSt ZnO time, strength, Percent, Percent on break, Elasticity, Shore Si02ator min. kg./c1n.2 lig/cm.2 Percent Percent hardness -6 D 1 "5 2 o a o40 157 27 40 595 so 7i 63 121 .4 DM .54 V 1. 28 60 153 30 55 568 37 7279 133 .08 V25 1. 28 40 106 37 66 533 39 79 93 157 .16 V25 1. 28 20 19131 61 685 37 79 84 151 .24 V25 1. 28 40 108 39 70 465 37 77 103 TABLE l0(EXAMPLE 10).- BUTADIENE-STYRENE-RUBBER BBI 150. VULCANIZATION TEMP. 160C.

Batch No. Heating Tearing Modulus, Elongation Modulus fillcr= Acceler- SSt Z110 time, strength, Percent, Percent on break, Elastieity, ShoreSiOz ator min, trg/em.2 kg./em.2 Percent; Percent hardness Example 11 Aseries of vulcanizates were produced using styrenebutadiene rubber BH150 containing 50 parts SiOZ as filler, 1.28 parts by weight of sulfurper parts by weight of the rubber and varying quantities of triazinecompound V19 and the abrasion resistance thereof tested in comparisonwith SiOZ filled vulcanizates obtained with conventional accelerators,and with HAF furnace black filled vulcanizates both with and withoutsoftener addition (Naftolen, a commercially available softener composedof a mixture of high molecular weight unsaturated hydrocarbone).

Vulcanized test plates dimensioned X 20 mm. were prepared from eachmixture and tested on an abrading apparatus of the type of theDunlop-Lambourne abrader at a surface velocity of about 80 km./h. Theabrasion loss was ascertained by weighing the test plates after 180,000revolutions. The abrasion loss suffered by the conventional HAF furnaceblack filled vulcanizate produced with a conventional accelerator butwithout the softener was set at 100% in the comparison made.

In the accompanying drawing:

FIG. 1 graphically shows the results of the abrasion tests; and

FIG. 2 graphically shows the typical Course of the torque measured in anelastometer test during vulcanization.

As can be seen from FIG. 1 the abrasion loss suffered by the HAF blackcontaining vulcanizate which also contained the softener was about 200%as compared with the 100% of the Vulcanizate in which the softener hadbeen omitted and that the SiOZ filled rubber composition produced withthe conventional accelerator was between 470 t0 500%. The curve obtainedwhen using varying quantities of compound V19 as accelerator showed thatconsiderably less abrasion loss was suffered in all instances than withthe conventionally vulcanized SiO2 lled rubber and that with quantitiesof compound V19 above about two parts per 100 parts of the rubber theabrasion loss was even less than that suffered by the conventionallyvulcanized furnace black filled rubber.

The effectiveness of the new vulcanizng agent systern according to theinvention was also shown by oscillating elastometer measurements. Insuch tests a cylindrical chamber of a diameter of 50 mm. and a height of1 mm. provided with a double cone shaped rotor was filled with themixture tested and such rotor turned 11.5 three times per minute. Thetorque required for turning the rotor was measured and recorded whilethe mixture was vulcanized at a constant temperature. The typical courseof the torque D required during the vulcanization time tis shownschematically in FIG. 2 of the drawing.

The torque difference Dai-Dn() depends upon the number of cross-linkinglocations introduced so that it is an indication of the effectiveness ofa vulcanizing agent system in comparison with others when the remainingcomponent of the mixtures are the same.

A series of such tests were carried out with conventional acceleratorsDM, CZ and M (mercaptobenzothia- Zol) and a large number of the triazinecompound accelerators according to the invention. The results of suchtests are given in Table 11. The triazine compounds concerned which werealready included in Table A are identified by the V numbers ascribed insuch table. Those not previously described in Table A bear an X numberand these are described at the end of the table. In each instance thesame butadiene-styrene rubber was used. The quantity of -iiller employedwas 50 parts by weight per 100 parts by weight of the rubber. Thequantity of triazine compound used was 5 mmol and the quantity of sulfur7.2 mmol. The vulcanization temperature used during the tests was C.

The first column of Table 11 gives the torque values in (Dt-DWG) 103[mkp.] obtained with HAF lled rubber modified with ZnO-l-stearic acid,the second column gives such values obtained with non-modified HAFfilled rubber and column 3 gives such values obtained with active Si02lilled rubber. The SiOz lemployed wasone having a BET specific surfacearea of 120 m.2/ g.

TABLE 11 Active SiO:

'00)1 Accelerator Z [mkpl HAF,

84 X:2-N-methyl-cyclohexylamino-4,-dimercaptos-triazine 96X=2-heXamethylenimino-4,-dimercapto-s-triazine s-triazine 85X=2dicyclohexylamino4,6-dimercapto-s-triazine 62X=2-cycloheXyl-i-propandammo-4,6-dimercaptohexamethylendiamine.

We claim:

1. In a pro-cess for vulcanizing a vulcanizable material selected fromthe group consisting of rubber and rubberlike elastomers which stillcontain ethylenic double bonds in admixture with a reenforcing filler,the step of employing a vulcanization system of (1) an effective amountof sulfur and (2) as an accelerator an effective amount of a mercaptotriazine compound of the formula wherein n is an average number from 1to about 20, X is selected from the group consisting of (1) alkyl, aryland aralkyl connected directly to the triazine ring, .(2) hydrogen,alkyl, alkenyl, aryl and aralkyl connected to the triazine ring over aheteroatom selected from the group consisting of -sand -o-, (3)hydrogen, alkyl, alkenyl. aryl and aralkyl connected to the triazinering over a hetero-atom lgroup selected from the group consisting of NH--NHSO2-, NH-NH* and NR6 wherein R6 is selected from the group consistingof alkyl, alkenyl and aryl and (4) and such radicals under (1), (2) and(3) in which the radical thereof selected from the group consisting ofalkyl, aryl and aralkyl is substituted by a substituent selected fromthe group consisting of -OH, -CN, SOSH and -COOH, each of Y and Zindividually is selected from the group consisting of (a) hydrogen (b)-S-R wherein R is selected from the group consisting of alkyl, aryl,aralkyl Z-benzothiazolyl and morpholino,

2. The process of claim 1 in which the quantity of the triazine compoundemployed is between 0.3 and 6 parts by weight and the quantity of sulfuris an eiTective amount up to 6 parts by weight per 100 parts 4by Weightof the vulcanizable material.

3. The process of claim 1 in which the quantity of the triazine compoundemployed is between 0.5 and 4.0 parts by Weight and the quantity ofsulfur is 0.5 to 3 parts by Weight per parts by Weight of thevulcanizable material.

4. The process of claim 1 in which the reinforcing iller is a linelydivided Iactive reinforcing silica.

5. The process of claim 1 in which said mercapto triazine compound is ofthe formula wherein X, Y and Z have the same meaning as in claim 1.

6. The process of claim 1 in which said mercapto triazine compound is ofthe formula wherein X has the same meaning as in claim 1.

7. The process of claim 1 in which said mercapto triazine compound is ofthe formula 1 5 l 6 wherein n is an average number from 1 to 10 whereinX 3,156,690 9/ 1964 Dexter et al 260-249.5 has the same meaning as inclaim 1. 3,245,992 4/1966 Dexter et al 260248 3,257,354 6/1966 Dexter etal 260-45.8 References Cited UNITED STATES PATENTS 5 MORRIS LIEBMAN,Primary Examiner. 2,914,503 9/ 1959 Pechukas 260-41.5 H. S. KAPLAN,Assistant Examiner.

3,156,689 9/1964 Dexter et al 1260-248

1. IN A PROCESS FOR VULCANIZING A VULCANIZABLE MATERIAL SELECTED FROMTHE GROUP CONSISTING OF RUBBER AND RUBBERLIKE ELASTOMERS WHICH STILLCONTAIN ETHYLENIC DOUBLE BONDS IN ADMIXTURE WITH A REENFORCING FILLER,THE STEP OF EMPLOYING A VULCANIZATION SYSTEM OF (1) AN EFFECTIVE AMOUNTOF SULFUR AND (2) AS AN ACCELERATOR AN EFFECTIVE AMOUNT OF A MERCAPTOTRIAZINE COMPOUND OF THE FORMULA